Condensed Consolidating Information (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Condensed Consolidating Financial Statements
Net sales	$ 1,911,738	$ 1,693,390	$ 5,508,774	$ 5,585,233
Costs of goods sold	1,714,546	1,536,989	4,987,626	5,045,432
Gross profit	197,192	156,401	521,148	539,801
Selling, general and administrative	83,919	83,680	242,445	243,565
Operating income	113,273	72,721	278,703	296,236
Interest expense, net of capitalized interest	30,970	41,490	97,064	123,708
Other (income) expense, net	(1,852)	24,010	(4,144)	32,366
Income before income taxes	84,155	7,221	185,783	140,162
Income taxes (benefit)	33,065	1,116	70,168	52,975
Net income	51,090	6,105	115,615	87,187
Net loss attributable to noncontrolling interests	6,396	6,728	19,044	15,793
Net income attributable to Steel Dynamics, Inc.	57,486	12,833	134,659	102,980
Parent
Condensed Consolidating Financial Statements
Net sales	902,280	785,168	2,566,286	2,625,152
Costs of goods sold	760,589	685,074	2,220,737	2,275,227
Gross profit	141,691	100,094	345,549	349,925
Selling, general and administrative	30,073	19,927	83,675	72,196
Operating income	111,618	80,167	261,874	277,729
Interest expense, net of capitalized interest	19,733	27,153	61,927	81,583
Other (income) expense, net	(2,423)	23,345	(4,776)	31,419
Income before income taxes	94,308	29,669	204,723	164,727
Income taxes (benefit)	24,930	(2,771)	41,945	31,809
Net income	69,378	32,440	162,778	132,918
Equity in net loss of subsidiaries	(11,892)	(19,607)	(28,119)	(29,938)
Net income attributable to Steel Dynamics, Inc.	57,486	12,833	134,659	102,980
Guarantors
Condensed Consolidating Financial Statements
Net sales	2,136,327	1,918,774	6,150,327	6,408,166
Costs of goods sold	2,025,470	1,823,447	5,840,025	6,106,504
Gross profit	110,857	95,327	310,302	301,662
Selling, general and administrative	55,348	53,023	164,104	160,513
Operating income	55,509	42,304	146,198	141,149
Interest expense, net of capitalized interest	10,561	13,997	33,351	41,208
Other (income) expense, net	631	434	645	(436)
Income before income taxes	44,317	27,873	112,202	100,377
Income taxes (benefit)	16,579	8,668	41,712	36,354
Net income	27,738	19,205	70,490	64,023
Net income attributable to Steel Dynamics, Inc.	27,738	19,205	70,490	64,023
Combined Non-Guarantors
Condensed Consolidating Financial Statements
Net sales	91,198	48,167	245,607	131,024
Costs of goods sold	114,408	69,520	318,163	189,477
Gross profit	(23,210)	(21,353)	(72,556)	(58,453)
Selling, general and administrative	2,622	14,032	7,433	20,940
Operating income	(25,832)	(35,385)	(79,989)	(79,393)
Interest expense, net of capitalized interest	1,915	1,619	5,405	5,068
Other (income) expense, net	(1,301)	(1,046)	(3,633)	(2,767)
Income before income taxes	(26,446)	(35,958)	(81,761)	(81,694)
Income taxes (benefit)	2,004	73	4,085	444
Net income	(28,450)	(36,031)	(85,846)	(82,138)
Net loss attributable to noncontrolling interests	6,396	6,728	19,044	15,793
Net income attributable to Steel Dynamics, Inc.	(22,054)	(29,303)	(66,802)	(66,345)
Consolidating Adjustments
Condensed Consolidating Financial Statements
Net sales	(1,218,067)	(1,058,719)	(3,453,446)	(3,579,109)
Costs of goods sold	(1,185,921)	(1,041,052)	(3,391,299)	(3,525,776)
Gross profit	(32,146)	(17,667)	(62,147)	(53,333)
Selling, general and administrative	(4,124)	(3,302)	(12,767)	(10,084)
Operating income	(28,022)	(14,365)	(49,380)	(43,249)
Interest expense, net of capitalized interest	(1,239)	(1,279)	(3,619)	(4,151)
Other (income) expense, net	1,241	1,277	3,620	4,150
Income before income taxes	(28,024)	(14,363)	(49,381)	(43,248)
Income taxes (benefit)	(10,448)	(4,854)	(17,574)	(15,632)
Net income	(17,576)	(9,509)	(31,807)	(27,616)
Equity in net loss of subsidiaries	11,892	19,607	28,119	29,938
Net income attributable to Steel Dynamics, Inc.	$ (5,684)	$ 10,098	$ (3,688)	$ 2,322